script to check the SSL certificate, with instructions for turning the self-signed certificate into a properly signed certificate

* Created a new Python/flask-based management daemon.
* Moved the mail user management core code from tools/mail.py to the new daemon.
* tools/mail.py is a wrapper around the daemon and can be run as a non-root user.
* Adding a new initscript for the management daemon.
* Moving dns_update.sh to the management daemon, called via curl'ing the daemon's API.

This also now runs the DNS update after mail users and aliases are added/removed,
which sets up new domains' DNS as needed.

remove permit_dnswl_client because postfix has odd behavior when an IP address is not listed: it turns all bounces into deferrals (retry)

partially reverts 6d473f81

test_mail: if EHLO test fails continue testing the rest, since user may be waiting on DNS propagation

add more postfix rules: reject_non_fqdn_sender, reject_unknown_sender_domain, reject_rhsbl_sender, and permit_dnswl_client

test_dns: properly test the non-primary domain of a box (for email addresses on domains besides PUBLIC_HOSTNAME)

DKIM: For the benefit of ADSP and DMARC (not yet impl), each sending domain should be its signing domain

See http://phusion.github.io/baseimage-docker/ for why the stock Ubuntu
image from Docker is not good enough for a complex system.

Thanks to @pjz for updating the base image for Ubuntu 14.04 and starting
the service scripts.

see #16; merges #49

* let the base image's system services manager handle it
* move our container start script to occur before system services are started

our trees had diverged, various conflicts resolved

docker: re-run the start script on the container's first run because it won't know its hostname or IP address until then

don't ask the user to create an email account if the shell is non-interactive and provide a better default for the domain name

docker: disable the ufw firewall because it is not supported in a docker container and produces a lot of error output (by reverting a510e08f and setting an environment variable)